1. Field of the Invention
The present invention relates to the field of electronic illumination systems and more specifically, to fluorescent lighting systems. The present invention provides a high efficiency, fluorescent lighting system which in a preferred embodiment is capable of providing three levels of illumination.
2. Background Discussion
Fluorescent lamps are well known illumination devices throughout the lighting industry. A fluorescent lamp is a particular type of electrical load which possesses an electrical characteristic known as "a negative resistance". That is, a high voltage is required to start the lamp and, once started, a lesser voltage is required to sustain its operation. Two types of fluorescent lamps, the "instant-start" and "rapid-start", are commonly used in existing light fixtures. With the instant-start lamp, a special electron emitting cathode emits electrons under the influence of a high voltage applied across the lamp terminals, without the need for preheating the lamp cathodes. With the rapid-start lamp, heaters or filaments, through which electrical current is passed, heat the cathodes to a sufficiently emissive temperature. In practice, both rapid-start and instant start fluorescent lamps are used with solid-state electronic ballasts which incorporate inverter-oscillator type circuits. These circuits, made of transistors and other semiconductor devices, transform low AC or DC voltages into high voltage required to operate one or more fluorescent lamps Modern AC solid-state ballasts also provide a degree of regulation of lamp current against line variations from the power supply.
Solid-state electronic ballasts are commercially available for one, two, three or four lamp configurations. The four-lamp ballast is generally considered the most energy efficient ballast available. Unfortunately, the three-lamp parabolic fixture is generally considered to be the most energy efficient fluorescent lamp fixture available. Until now, methods of connecting the most energy efficient ballast with the most energy efficient lamp fixture has eluded designers in the lighting industry, with attempts often resulting in design configurations which are costly, complicated and generally less efficient than desired.
Fluorescent lighting systems which provide more than one level of illumination have also proved to be expensive, complicated, and generally less efficient than desired, mostly because a separate ballast/lamp circuit is required for each desired level of illumination.